336 L. D. CAIKNES EROSION AND EQUIPLAXATION IN ALASKA 



The Carboniferous beds occur only in the souilierii portion of the dis- 

 trict, where they outcrop throughout an area not exceeding lU or 1'^ 

 square miles in extent. They haA^ an aggregate thickness of at least 1,500 

 feet and consist mainly of limestones, cherts, and cherty conglomerates, 

 all three of which occur, in places, intimately associated. The limestones 

 are generally quite crystalline and range from nearly white through 

 \'arious shades of grey to almost black in color, occasional reddish mem- 

 bers being also noted. The upper limestone beds nearly everywhere con- 

 tain chert pebbles, which, in places, constitute the cherty conglomerates 

 of this series, and all gradations occur from a limestone including only 

 occasional chert pebbles to a cherty conglomerate with a siliceous matrix 

 and containing no perceptible lime. The chert pebbles are well rounded, 

 and dominantly about the size of marbles, but some were noted as large 

 as 1% to 2 inches in diameter. In color most of the pebbles are grey, 

 but occasionally quite black individuals were noticed. Beds of pure mas- 

 sive chert, similar in appearance to that composing the conglomerate 

 pebbles, occur in places, but are not nearly so extensive as the limestone 

 or conglomerate members. Fossils were obtained in a number of places 

 from the limestone beds of this series, and all have been identified as 

 being of Carboniferous age. 



The Mesozoic beds extend over about two-thirds of the entire area 

 under consideration, and consist chiefly of slates, phyllites, and quartz- 

 ites, with also occasional sandstone, shale, dolomite, and magnesite beds. 



The slates vary greatly in color, ranging from black to various shades 

 of grey, green, red, o'r brown. They have everywhere a decidedly sec- 

 ondary induced cleavage, and generally break readily into thin plates 

 from one to several feet in diameter and as thin as one-sixteentli of an 

 inch, or even less. Probably the most noticeable and persistent beds are 

 certain beautifully banded red and green members, the alternate bands 

 of which are in places extremely thin and delicate and not more than 

 one-fourth of an inch to 2 inches in j:hickness, and frequently much less, 

 presenting thus a decidedly ribbon-like appearance. 



The phyllites also vary considerably in color, but are generally some 

 shade of grey, although occasionally greenish, brownish, or black mem- 

 bers were noted. These rocks are distinguished from the slates by con- 

 taining more mica, and being, generally, somewhat coarser textured. In 

 places, the phyllites are much crumpled, folded, and distorted — isoclinal 

 and even closed folds having been frequently noted in hand specimens. 

 These rocks, also, wherever found, break readily along their cleavage 

 planes, thus giving rise to the large thin slabs which are everywhere in 

 evidence where these beds outcrop. 



